1. Field of the Invention
The present invention relates to methods and apparatuses for calculating/controlling power generation torque to be used for generating power; this power is supplied to electrical loads of a vehicle, such as a passenger vehicle or a commercial vehicle.
2. Description of the Related Art
In modern vehicles, such as passenger and commercial vehicles, a plurality of electrical loads requiring power have been installed. A power supply system has been used to meet the power requirement of each load installed in a vehicle. The main component of the power supply system is an alternator. The alternator has an exciting winding (field winding) and can regulate an exciting current flowing therethrough so as to control the alternator output (output power). The alternator output is supplied to the loads and a battery in which a DC voltage based on the alternator output is charged.
In such a power supply system, it is important to detect and control power generation torque so as to stabilize rotation of the engine crankshaft of the vehicle.
One example of methods of detecting the power generation torque has been known. The method is to detect the power generation torque based on an exciting current and the number of revolution of an alternator, or the output voltage of the alternator in addition to them. The method is disclosed in the Japanese Unexamined Patent Publications No. 2003-74388 and No. 2003-284257.
The power-generation torque detecting method disclosed in the Patent Publications is for example to:
obtain a relationship between the power-generation torque and the exciting current and/or the alternator rotation to prepare a map representing the obtained relationship;
detect a value of the exciting current or that of the number of revolution of the alternator; and
detect a value of the power-generation torque corresponding to the detected value of the exciting current or the number of revolution of the alternator based on the map.
Control of the exciting current based on the detected value of the power-generation torque can prevent the power-generation torque from excessively increasing. In addition, control of the engine using the detected value of the power-generation torque permits the engine speed to be stabilized even with the engine at an idle.
On the other hand, in such a power supply system, various types of energy-saving techniques have been installed. Japanese Unexamined Patent Publication No. 2003-244998 discloses one example of the energy-saving techniques.
In the Patent Publication No. 2003-244998, while throttling down an engine, the output voltage of an alternator is increased so as to forcibly charge a battery depending on the increased voltage. When fuel supply is normally supplied to the engine after the forced charging, reduction in the output voltage of the alternator for a predetermined period allows the alternator not to charge the battery, which causes the forcibly charged voltage to be supplied from the battery to electrical loads.
The predetermined period will be referred to as non-power generation period, the operation mode of the power supply system during the non-power generation period will be referred to as non-power generation mode, and the disclosed energy-saving technique disclosed in the Patent Publication No. 2003-244998 will be referred to as non-power generation regenerative braking technique.
In the power-generation torque detecting method disclosed in the Patent Publications No. 2003-74388 and No. 2003-284257, change in the temperature of stator windings wound around a stator of the alternator is unconsidered. For this reason, there is the possibility that a degree of accuracy for detecting a value of the power-generation torque may be low.
For example, if the stator-winding temperature at the map preparing time is different from that at the time of actually detecting a value of the power-generation torque, the value of the power-generation torque at the map preparing time may be different from that of the power-generation torque at the alternator-torque detecting time even though the values of the exciting current and/or the alternator rotation stay the same.
Particularly, resistances across the stator windings widely depend on the temperature thereof. This may cause the value of the power-generation torque to undergo a great change depending on an amount of the current flowing through the field winding between the map preparing time and the alternator-torque detecting time even though the values of the exciting current and/or the rotation of the rotor stay the same.
On the other hand, in the non-power generation regenerative braking technique disclosed in the Patent Publication No. 2003-244998, while the power supply system operates in the non-power generation mode, the value of the power-generation torque may reach zero because the battery voltage is higher than the output voltage of the alternator. In this state, when instructions to generate a great value of the power-generation torque is input to the power supply system, high inductance of the field winding may make it difficult for the alternator to generate the indicated great value of the power-generation torque. This may cause the alternator's response to torque-change instructions to deteriorate. This may have a negative influence on the realization of a control system for controlling both the power-generation torque and the engine torque to respond to the rapid changes in the vehicle required torque, thereby improving the fuel efficiency.
The problem set forth above may also appear in retuning the power supply system to the torque control mode after causing the alternator not to charge the battery under acceleration.
In order to remedy the problem, the Patent Publication No. 2003-244998 discloses a method of causing the exciting current to flow through the exciting winding within the range in which the power-generation torque is kept to zero during the non-power generation period.
The method, however, may cause return of the power supply system to the torque control mode to be delayed. This may increase waste of current flowing through the exciting winding, causing power loss and the exciting winding to rise in temperature.